﻿/*
 * Copyright 2008 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using com.google.zxing;
using com.google.zxing.common; 

namespace com.google.zxing.datamatrix.detector
{
    /**
     * <p>Encapsulates logic that can detect a Data Matrix Code in an image, even if the Data Matrix Code
     * is rotated or skewed, or partially obscured.</p>
     *
     * @author Sean Owen
     */
    public sealed class Detector
    {
          private static  int MAX_MODULES = 32;

          // Trick to avoid creating new int objects below -- a sort of crude copy of
          // the int.valueOf(int) optimization added in Java 5, not in J2ME
          private static  int[] intS =
              {0, 1, 2, 3, 4};

          private  MonochromeBitmapSource image;

          public Detector(MonochromeBitmapSource image) {
            this.image = image;
          }

          /**
           * <p>Detects a Data Matrix Code in an image.</p>
           *
           * @return {@link DetectorResult} encapsulating results of detecting a QR Code
           * @throws ReaderException if no Data Matrix Code can be found
           */
          public DetectorResult detect() {

            if (!BlackPointEstimationMethod.TWO_D_SAMPLING.Equals(image.getLastEstimationMethod())) {
              image.estimateBlackPoint(BlackPointEstimationMethod.TWO_D_SAMPLING, 0);
            }

            int height = image.getHeight();
            int width = image.getWidth();
            int halfHeight = height >> 1;
            int halfWidth = width >> 1;
            int iSkip = Math.Max(1, height / (MAX_MODULES << 3));
            int jSkip = Math.Max(1, width / (MAX_MODULES << 3));

            int minI = 0;
            int maxI = height;
            int minJ = 0;
            int maxJ = width;
            ResultPoint pointA = findCornerFromCenter(halfHeight, -iSkip, minI, maxI, halfWidth,      0, minJ, maxJ, halfWidth >> 1);
            minI = (int) pointA.getY() - 1;
            ResultPoint pointB = findCornerFromCenter(halfHeight, 0,      minI, maxI, halfWidth, -jSkip, minJ, maxJ, halfHeight >> 1);
            minJ = (int) pointB.getX() - 1;
            ResultPoint pointC = findCornerFromCenter(halfHeight, 0,      minI, maxI, halfWidth,  jSkip, minJ, maxJ, halfHeight >> 1);
            maxJ = (int) pointC.getX() + 1;
            ResultPoint pointD = findCornerFromCenter(halfHeight,  iSkip, minI, maxI, halfWidth,      0, minJ, maxJ, halfWidth >> 1);
            maxI = (int) pointD.getY() + 1;
            // Go try to find point A again with better information -- might have been off at first.
            pointA = findCornerFromCenter(halfHeight, -iSkip, minI, maxI, halfWidth,      0, minJ, maxJ, halfWidth >> 2);

            // Point A and D are across the diagonal from one another,
            // as are B and C. Figure out which are the solid black lines
            // by counting transitions
            System.Collections.ArrayList transitions = new System.Collections.ArrayList(4);
            transitions.Add(transitionsBetween(pointA, pointB));
            transitions.Add(transitionsBetween(pointA, pointC));
            transitions.Add(transitionsBetween(pointB, pointD));
            transitions.Add(transitionsBetween(pointC, pointD));
            Collections.insertionSort(transitions, new ResultPointsAndTransitionsComparator());

            // Sort by number of transitions. First two will be the two solid sides; last two
            // will be the two alternating black/white sides
            ResultPointsAndTransitions lSideOne = (ResultPointsAndTransitions) transitions[0];
            ResultPointsAndTransitions lSideTwo = (ResultPointsAndTransitions) transitions[1];

            // Figure out which point is their intersection by tallying up the number of times we see the
            // endpoints in the four endpoints. One will show up twice.
            System.Collections.Hashtable pointCount = new System.Collections.Hashtable();
            increment(pointCount, lSideOne.getFrom());
            increment(pointCount, lSideOne.getTo());
            increment(pointCount, lSideTwo.getFrom());
            increment(pointCount, lSideTwo.getTo());

            ResultPoint maybeTopLeft = null;
            ResultPoint bottomLeft = null;
            ResultPoint maybeBottomRight = null;
            System.Collections.IEnumerator points = pointCount.GetEnumerator();

            while (points.MoveNext()) {
              ResultPoint point = (ResultPoint) points.Current;
              int value = (int) pointCount[point];
              if (value == 2) {
                bottomLeft = point; // this is definitely the bottom left, then -- end of two L sides
              } else {
                // Otherwise it's either top left or bottom right -- just assign the two arbitrarily now
                if (maybeTopLeft == null) {
                  maybeTopLeft = point;
                } else {
                  maybeBottomRight = point;
                }
              }
            }

            if (maybeTopLeft == null || bottomLeft == null || maybeBottomRight == null) {
              throw new ReaderException();
            }

            // Bottom left is correct but top left and bottom right might be switched
            ResultPoint[] corners = { maybeTopLeft, bottomLeft, maybeBottomRight };
            // Use the dot product trick to sort them out
            GenericResultPoint.orderBestPatterns(corners);

            // Now we know which is which:
            ResultPoint bottomRight = corners[0];
            bottomLeft = corners[1];
            ResultPoint topLeft = corners[2];

            // Which point didn't we find in relation to the "L" sides? that's the top right corner
            ResultPoint topRight;
            if (!pointCount.ContainsKey(pointA)) {
              topRight = pointA;
            } else if (!pointCount.ContainsKey(pointB)) {
              topRight = pointB;
            } else if (!pointCount.ContainsKey(pointC)) {
              topRight = pointC;
            } else {
              topRight = pointD;
            }

            // Next determine the dimension by tracing along the top or right side and counting black/white
            // transitions. Since we start inside a black module, we should see a number of transitions
            // equal to 1 less than the code dimension. Well, actually 2 less, because we are going to
            // end on a black module:

            // The top right point is actually the corner of a module, which is one of the two black modules
            // adjacent to the white module at the top right. Tracing to that corner from either the top left
            // or bottom right should work here, but, one will be more reliable since it's traced straight
            // up or across, rather than at a slight angle. We use dot products to figure out which is
            // better to use:
            int dimension;
            if (GenericResultPoint.crossProductZ(bottomLeft, bottomRight, topRight) <
                GenericResultPoint.crossProductZ(topRight, topLeft, bottomLeft)) {
              dimension = transitionsBetween(topLeft, topRight).getTransitions();
            } else {
              dimension = transitionsBetween(bottomRight, topRight).getTransitions();
            }
            dimension += 2;

            BitMatrix bits = sampleGrid(image, topLeft, bottomLeft, bottomRight, dimension);
            return new DetectorResult(bits, new ResultPoint[] {pointA, pointB, pointC, pointD});
          }

          /**
           * Attempts to locate a corner of the barcode by scanning up, down, left or right from a center
           * point which should be within the barcode.
           *
           * @param centerI center's i componennt (vertical)
           * @param di change in i per step. If scanning up this is negative; down, positive; left or right, 0
           * @param minI minimum value of i to search through (meaningless when di == 0)
           * @param maxI maximum value of i
           * @param centerJ center's j component (horizontal)
           * @param dj same as di but change in j per step instead
           * @param minJ see minI
           * @param maxJ see minJ
           * @param maxWhiteRun maximum run of white pixels that can still be considered to be within
           *  the barcode
           * @return a {@link ResultPoint} encapsulating the corner that was found
           * @throws ReaderException if such a point cannot be found
           */
          private ResultPoint findCornerFromCenter(int centerI, int di, int minI, int maxI,
                                                   int centerJ, int dj, int minJ, int maxJ,
                                                   int maxWhiteRun) {
            int[] lastRange = null;
            for (int i = centerI, j = centerJ;
                 i < maxI && i >= minI && j < maxJ && j >= minJ;
                 i += di, j += dj) {
              int[] range;
              if (dj == 0) {
                // horizontal slices, up and down
                range = blackWhiteRange(i, maxWhiteRun, minJ, maxJ, true);
              } else {
                // vertical slices, left and right
                range = blackWhiteRange(j, maxWhiteRun, minI, maxI, false);
              }
              if (range == null) {
                if (lastRange == null) {
                  throw new ReaderException();
                }
                // lastRange was found
                if (dj == 0) {
                  int lastI = i - di;
                  if (lastRange[0] < centerJ) {
                    if (lastRange[1] > centerJ) {
                      // straddle, choose one or the other based on direction
                      return new GenericResultPoint(di > 0 ? lastRange[0] : lastRange[1], lastI);
                    }
                    return new GenericResultPoint(lastRange[0], lastI);
                  } else {
                    return new GenericResultPoint(lastRange[1], lastI);
                  }
                } else {
                  int lastJ = j - dj;
                  if (lastRange[0] < centerI) {
                    if (lastRange[1] > centerI) {
                      return new GenericResultPoint(lastJ, dj < 0 ? lastRange[0] : lastRange[1]);
                    }
                    return new GenericResultPoint(lastJ, lastRange[0]);
                  } else {
                    return new GenericResultPoint(lastJ, lastRange[1]);
                  }
                }
              }
              lastRange = range;
            }
            throw new ReaderException();
          }

          /**
           * Increments the int associated with a key by one.
           */
          private static void increment(System.Collections.Hashtable table, ResultPoint key) {
            int value = (int) table[key];
            table[key] = value.Equals(null) ? intS[1] : intS[value + 1];
            //table.put(key, value == null ? intS[1] : intS[value.intValue() + 1]);
          }

          /**
           * Computes the start and end of a region of pixels, either horizontally or vertically, that could be
           * part of a Data Matrix barcode.
           *
           * @param fixedDimension if scanning horizontally, this is the row (the fixed vertical location) where
           *  we are scanning. If scanning vertically it's the colummn, the fixed horizontal location
           * @param maxWhiteRun largest run of white pixels that can still be considered part of the barcode region
           * @param minDim minimum pixel location, horizontally or vertically, to consider
           * @param maxDim maximum pixel location, horizontally or vertically, to consider
           * @param horizontal if true, we're scanning left-right, instead of up-down
           * @return int[] with start and end of found range, or null if no such range is found (e.g. only white was found)
           */
          private int[] blackWhiteRange(int fixedDimension, int maxWhiteRun, int minDim, int maxDim, bool horizontal) {

            int center = (minDim + maxDim) / 2;

            BitArray rowOrColumn = horizontal ? image.getBlackRow(fixedDimension, null, 0, image.getWidth())
                                              : image.getBlackColumn(fixedDimension, null, 0, image.getHeight());

            // Scan left/up first
            int start = center;
            while (start >= minDim) {
              if (rowOrColumn.get(start)) {
                start--;
              } else {
                int whiteRunStart = start;
                do {
                  start--;
                } while (start >= minDim && !rowOrColumn.get(start));
                int whiteRunSize = whiteRunStart - start;
                if (start < minDim || whiteRunSize > maxWhiteRun) {
                  start = whiteRunStart + 1; // back up
                  break;
                }
              }
            }
            start++;

            // Then try right/down
            int end = center;
            while (end < maxDim) {
              if (rowOrColumn.get(end)) {
                end++;
              } else {
                int whiteRunStart = end;
                do {
                  end++;
                } while (end < maxDim && !rowOrColumn.get(end));
                int whiteRunSize = end - whiteRunStart;
                if (end >= maxDim || whiteRunSize > maxWhiteRun) {
                  end = whiteRunStart - 1;
                  break;
                }
              }
            }
            end--;

            if (end > start) {
              return new int[] { start, end };
            } else {
              return null;
            }
          }

          private static BitMatrix sampleGrid(MonochromeBitmapSource image,
                                              ResultPoint topLeft,
                                              ResultPoint bottomLeft,
                                              ResultPoint bottomRight,
                                              int dimension) {

            // We make up the top right point for now, based on the others.
            // TODO: we actually found a fourth corner above and figured out which of two modules
            // it was the corner of. We could use that here and adjust for perspective distortion.
            float topRightX = (bottomRight.getX() - bottomLeft.getX()) + topLeft.getX();
            float topRightY = (bottomRight.getY() - bottomLeft.getY()) + topLeft.getY();

            // Note that unlike in the QR Code sampler, we didn't find the center of modules, but the
            // very corners. So there is no 0.5f here; 0.0f is right.
            GridSampler sampler = GridSampler.Instance;
            return sampler.sampleGrid(
                image,
                dimension,
                0.0f,
                0.0f,
                dimension,
                0.0f,
                dimension,
                dimension,
                0.0f,
                dimension,
                topLeft.getX(),
                topLeft.getY(),
                topRightX,
                topRightY,
                bottomRight.getX(),
                bottomRight.getY(),
                bottomLeft.getX(),
                bottomLeft.getY());
          }

          /**
           * Counts the number of black/white transitions between two points, using something like Bresenham's algorithm.
           */
          private ResultPointsAndTransitions transitionsBetween(ResultPoint from, ResultPoint to) {
            // See QR Code Detector, sizeOfBlackWhiteBlackRun()
            int fromX = (int) from.getX();
            int fromY = (int) from.getY();
            int toX = (int) to.getX();
            int toY = (int) to.getY();
            bool steep = Math.Abs(toY - fromY) > Math.Abs(toX - fromX);
            if (steep) {
              int temp = fromX;
              fromX = fromY;
              fromY = temp;
              temp = toX;
              toX = toY;
              toY = temp;
            }

            int dx = Math.Abs(toX - fromX);
            int dy = Math.Abs(toY - fromY);
            int error = -dx >> 1;
            int ystep = fromY < toY ? 1 : -1;
            int xstep = fromX < toX ? 1 : -1;
            int transitions = 0;
            bool inBlack = image.isBlack(steep ? fromY : fromX, steep ? fromX : fromY);
            for (int x = fromX, y = fromY; x != toX; x += xstep) {
              bool isBlack = image.isBlack(steep ? y : x, steep ? x : y);
              if (isBlack == !inBlack) {
                transitions++;
                inBlack = isBlack;
              }
              error += dy;
              if (error > 0) {
                y += ystep;
                error -= dx;
              }
            }
            return new ResultPointsAndTransitions(from, to, transitions);
          }

          /**
           * Simply encapsulates two points and a number of transitions between them.
           */
          private class ResultPointsAndTransitions {
            private  ResultPoint from;
            private  ResultPoint to;
            private  int transitions;

            public ResultPointsAndTransitions(ResultPoint from, ResultPoint to, int transitions) {
              this.from = from;
              this.to = to;
              this.transitions = transitions;
            }

            public ResultPoint getFrom() {
              return from;
            }
            public ResultPoint getTo() {
              return to;
            }
            public int getTransitions() {
              return transitions;
            }
            public String toString() {
              return from + "/" + to + '/' + transitions;
            }
          }

          /**
           * Orders ResultPointsAndTransitions by number of transitions, ascending.
           */
          private class ResultPointsAndTransitionsComparator : Comparator {
            public int compare(Object o1, Object o2) {
              return ((ResultPointsAndTransitions) o1).getTransitions() - ((ResultPointsAndTransitions) o2).getTransitions();
            }
          }
    }
}
